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This paper analyzes the main kinetic features of biomass pyrolysis, devolatilization, and the gas phase reactions of the released species. Three complex steps are faced in sequence: the characterization of biomasses, the description of the release of the species, and finally, their chemical evolution in the gas phase. Biomass is characterized as a mixture of reference constituents: cellulose, hemicellulose, and lignin. This assumption is verified versus experimental data, mainly relating to thermal degradation of different biomasses. Devolatilization of biomasses is a complex process in which several chemical reactions take place in both the gas and the condensed phase alongside the mass and thermal resistances involved in the pyrolysis process. A novel characterization of the released species is applied in the proposed devolatilization models. The successive gas phase reactions of released species are included into an existing detailed kinetic scheme of pyrolysis and oxidation of hydrocarbon fuels. Comparisons with experimental measurements in a drop tube reactor confirm the high potentials of the proposed modeling approach.

The kinetic modeling of the pyrolysis and combustion of liquid transportation fuels is a very complex task for two different reasons: the challenging characterization of the complex mixture of several hydrocarbon isomers and the complexity of the oxidation mechanisms of large hydrocarbon and oxygenated molecules. While surrogate mixtures of reference components allow to tackle the first difficulty, the complex behavior of the oxidation mechanisms is mostly overcome by reducing the total number of involved species by adopting a lumping approach. After a first investigation of the different liquid fuels (gasoline, kerosene, and diesel fuels), a short discussion on the lumping techniques allows to highlight the advantages of this approach. The lumped POLIMI pyrolysis and oxidation mechanism of hydrocarbon and oxygenated fuels is then used for generating several skeletal mechanisms for typical surrogate mixtures, moving from pure n-heptane up to heavy diesel fuels. These skeletal models are simply reduced with a reaction flux analysis, and they involve between 100 and 200 species. While these sizes already allow detailed computational fluid dynamics (CFD) calculations in internal combustion engines, further reduction phases are necessary when the interest is toward more complex CFD computations. To maintain the standard structure of the skeletal mechanisms, successive reduction phases are not considered. Moreover, new regulations pushed toward a greater use of renewable fuels. For these reasons, the skeletal models are also extended to biogasolines including methanol, ethanol, and n-butanol. Similarly, skeletal models of diesel and biodiesel fuels, including methyl esters, are also provided. Several comparisons with experimental data and complete validations in the operating range of internal combustion engines are also reported. The whole set of comparisons with experimental data obtained in a wide range of conditions not only validate the reduced models of specific transportation fuels but also the complete kinetic scheme POLIMI 1404

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The main goal of this paper is the extension of a general semidetailed kinetic scheme of hydrocarbon oxidation to heavy fuels. Taking previous n-pentane and n-heptane kinetic modeling experience a step further, a lumped approach was systematically applied to n-decane, n-dodecane, and n-hexadecane. These semidetailed submodels for higher n-alkanes are directly derived from the complete set of primary propagation reactions, automatically generated by the MAMOX++ program on the basis of a small set of reference kinetic parameters. This proposed approach and lumped model are supported by a wide range of comparisons with a large variety of experimental measurements relating to stirred and flow reactors, premixed and diffusion flames, and fuel droplet combustion under microgravity conditions. The general agreement obtained in the overall range of conditions further confirms and supports the soundness of the small set of kinetic parameters used as reference values for the different classes of the primary propagation reactions of alkanes. This analysis demonstrates that heavy n-alkanes display the same kinetic behavior in both the high- and the low-temperature regions, thus allowing a direct extension of the overall kinetic scheme. The limitations and the advantages of the lumped approach as compared to detailed kinetic schemes are also discussed.

Pyrolysis of centimeter-scale wood particles is of practical interest and provides a sensitive test of pyrolysis models, especially their thermochemistry. In this paper we present an updated comprehensive pyrolysis model including chemical reactions and transport of heat and species, implemented independently in two different software environments. Results of the model are compared to experimental results of three independent sets of centimeter-scale experiments. Temperatures, mass losses, and rate of production of several gaseous and light tar species are included in the comparisons. Predictions and experiments agree qualitatively and in most cases have reasonable quantitative agreement. We also report comparisons of model predictions to literature data obtained in other regimes (thermogravimetric analysis and omogeneous tar cracking) in order to demonstrate that predictive capabilities of the model have not been compromised by the modifications presented here